A) Field of the Invention
The present invention relates to an electrochromic display (ECD).
B) Description of the Related Art
One known non-emissive display that utilizes a color change phenomenon of a substance due to an electrochemical reversible reaction (an electrolytic oxidation-reduction reaction) caused by the application of a voltage is an electrochromic display (see, for example, Japanese Examined Patent Application Publication No. 1-28927).
Since an electrochromic display is driven by a current, the electric wiring (lead wire) resistance of the electrochromic display should be reduced. For example, in the display of characters, a higher lead resistance of a display electrode can result in lower contrast (a lower color density) and a higher driving voltage of a more distant pixel.
In order to reduce lead resistance, a lead wire for a display electrode may have a large width but should be designed so as not to interfere (overlap) with a lead wire for a counter electrode. Thus, the width of the lead wire for a display electrode is limited. More specifically, when lead wires for a display electrode and a counter electrode intersect on a cell surface, the intersection also acts as a pixel and causes misregistration.
A lead wire may be made of a material having a low specific resistance. However, in an electrochromic display, an electrode disposed on at least one side of its substrate must be made of a transparent electroconductive material, such as ITO. It is therefore difficult to prevent adverse effects of distant pixels on display images.
In electrochromic displays, edges of pixels (edges of electrodes) generally tend to become darker in color. In particular, this results in variations in the display of characters and low display quality. Variations in the display of characters are particularly noticeable in pixels having a large display area.
The invention according to Japanese Examined Patent Application Publication No. 1-28927 can be applied to electrochromic displays that cause coloration and decoloration of an interfacial film but cannot be applied to electrochromic displays that cause coloration and decoloration in the bulk. Furthermore, because of difficulty in patterning a second electrode, only static driving is possible (duty driving is impossible).